Voltage drop with mixed wire sizes

[boatpoker]

Originally Posted by Bowdrie

True enough.
A reasonable analogy can be made with hose.
Blow thru a 6in long piece of 1/2 inch hose.
Now try and blow thru a 50-foot length of it.
Nevertheless, one has more peace of mind when ALL wires are oversize for the job they do.
An old Naval Architect I knew told me "There is NO place on a boat for any wire smaller that 14 gage".
Before someone gets their knickers in a twist, he was not talking about all the data cables people string all thru their boats.

Totally agree. Even tho' I was ABYC Electrically Certified. I ignored those tables on my own boat and have always used the biggest wire I could fit.

[smac999]

every 30a atc fuse holder I've seen latly is 12awg.

105c 12awg single stranded, in engine room is rated for 38a as per abyc. and that is a constant rating. starter solenoid is 1 sec long.

personly I would avoid running a 30a fuse in any atc holder. I try to stick to max 10a for glass and 20a for atc. I would consider putting an MRBF fuse right on the start post for it instead.

[boatpoker]

I use four of these on my solar system with #10AWG. Makes more sense than fuses to me.
Ad says 12AWG but #10 fits

https://www.amazon.com/dp/B0BZHHHQZ2...9kZXRhaWw&th=1

[s/v Jedi]

The SaltEnjoyer is simply wrong, don’t follow those recommendations.

If you just think about it: a 30A fuse holder comes with 12 gauge pigtails… then you should maybe get a hint that 12 gauge can do 30A?!

In fact, 12 gauge can do 45A and 10 gauge can do 60A. Yes, for long circuits it isn’t about ampacity but about voltage drop so simply add the 10 gauge section voltage drop to the short 12 gauge section voltage drop to get the total.

So in short: look up the wire ampacity to find the minimum required wire size and matching fuse value, then use the voltage drop calculator to see how much bigger you need to make the circuit wiring to limit voltage drop for your circuit.

Here is an old URL that has kept working for 10 years so pretty stable: https://www.westmarine.com/west-advi...-Ampacity.html

[Putt-Putt]

Originally Posted by boatpoker

I use four of these on my solar system with #10AWG. Makes more sense than fuses to me.
Ad says 12AWG but #10 fits

Do these $9, 30 to 150 amp breakers carry any certification, UL, IEC, CSA, ABS, anything?

Must have something if used (even on solar) by boatpoker.

[NorthCoastJoe]

Why all the heavy wire. I have a Yanmar 3gm30f

From starter + terminal to a relay on the other side of the relay circuit to the solenoid terminal all in 10 gauge.

Mount the relay close to the starter, less than a foot of wire 10 gauge used here.

The wire from the start button to the relay can be much smaller. A generic 30 amp relay should cost less than $10.

[Cheechako]

A better question may be: Why is there a fuse on your starter solenoid? I dont remember ever having one for that....?
And the comments about the smaller gauge wire capacity being effected by length are right. If it's very short it's not an issue.

[team karst]

Originally Posted by Cheechako

A better question may be: Why is there a fuse on your starter solenoid? I dont remember ever having one ….

The feed from starter terminal to dash controls are usually fused.

[Montanan]

Assuming 12 volt system, 3% voltage drop, a 30 ampacity as per rating of the stated desired chosen fuse, and 40 feet length [total distance from and to the battery and the starter.]

Further assumptions:


105°C insulation rating: All Ancor wire uses 105°C insulation rating. Lower temperature insulation cannot handle as much current
AWG wire sizes, not SAE: All Ancor wire uses AWG wire sizes. SAE wire sizes are 6 to 12 percent smaller, carry proportionally less current, and have greater resistance
Wires are not run in engine spaces: Maximum current is 15 percent less in engine spaces, which are assumed to be 20°C hotter than non-engine spaces (50°C vs. 30°C).
Conductors are not bundled: If three conductors are bundled, reduce maximum amperage by 30 percent. If 4–6 conductors are bundled, reduce maximum amperage by 40 percent. If 7–24 conductors are bundled, reduce amperage by 50 percent.

Per West Marine Wire Size and Ampacity Chart:

https://www.westmarine.com/west-advi...-Ampacity.html

The wire size should be AWG 4.

[Montanan]

Reference starter amperage draw for Yanmar 3GM30 per CF post

https://www.cruisersforum.com/forums...nt-240402.html

60 Amps if engine is decompressed, upwards of 460 amps is fully loaded.

[markcouz]

Starter solenoid.... sheesh, nobody reads!

[sinnerman]

Originally Posted by Wolfe10

Another solution to voltage drop in high amp/long wire run circuits is to use a RELAY with the switch/key serving to close the relay. The power IN and OUT of the relay in the appropriate gauge wire and much shorter wire run.


With Relays, bigger is better. 40 amp 12 VDC relays are under $10.

Very good point.

Especially with the GLOW PLUG circuit which takes beaucoup amperes.

my two cents

cheers

[sinnerman]

On my boat's engine panel harness, the 12vdc hot & negative wires as well as the starter solenoid and glow plug wires are all 10 AWG. About 15 feet panel to engine.

I have a 30amp fuse holder with 12 AWG pigtails on the 12vdc hot wire on my engine harness and have had no issues. Just keep the pigtails of 12 AWG as short as possible.

My fuse is right at the source of the 12vdc supply.

The larger 10AWG wire gauge is to help reduce the wire voltage loss (under high current) over the length of the harness to and from the control panel.

I am probably using the same fuse holder as you:
https://www.bluesea.com/products/506...TC_Fuse_Holder

My two cents

Thanks,
Andy[/QUOTE]

[Shaneesprit]

Perfectly fine and often required to increase wire size for Voltage Drop - So yes short wire is ok as long as the fuse is related for the smallest wire and it can carry the current.

If it were me I would try and install a slave relay and only have the high current loads ( 25 - 30A ) near to the battery / Engine.
Saves copper and also more reliable also more likely to work if one day in the future you find your batteries flat.

[CharlieJ]

@Montanan #25:

If 4–6 conductors are bundled, reduce maximum amperage by 40 percent. If 7–24 conductors are bundled, reduce amperage by 50 percent.

You are on the right track but per ABYC E-11; Table 4C, 4D and 4E; bundling for more than three current carrying conductors is only considered for AC wiring.